The present invention relates to electronic power supplies. More particularly, but not by way of limitation, the present invention relates to a power supply which would provide a pre-determined voltage output from batteries, which themselves could vary in number, voltage or level of charge.
As will become apparent from the discussion below, there is generally a need for a boost regulator for battery-operated devices whereby the output voltage will remain constant over substantially the entire discharge cycle of the battery. There are several areas where this is especially true such as battery operated lighting used in the motion picture and television industries and for certain battery operated, motorized devices.
U.S. Pat. No. 6,246,184 issued to Salerno represents a step in the right direction. Salerno discloses a boost regulator for a conventional battery operated flashlight wherein, after the battery voltage falls 15-20%, the boost regulator kicks in to provide a substantially constant voltage until a major portion of the stored battery energy has been consumed. While Salerno provides a marked improvement for conventional hand-held flashlights, the improvements are limited to devices where the initial battery voltage is the same as the lamp voltage. In addition, the device of Salerno is clearly drawn to conventional lamps, which employ a filament. Such lamps are inefficient, not daylight balanced, and somewhat fragile compared to alternative lamps.
Continuous arc xenon bulbs (hereinafter referred to as a “xenon lamp”) provide bright, stable, daylight balanced light at power levels from a few watts up to tens of thousands of watts. Such bulbs are widely accepted in architectural, entertainment, and medical applications. Typically, such bulbs require a moderate DC voltage (on the order of 12 to 50 volts) at a relatively high current for steady-state operation. Some longer arc bulbs require higher voltages. Thus, a ballast or power supply is normally required for operation of a xenon bulb. Presently, xenon power supplies may be logically divided into two distinct groups, those that operate on line voltages and those that operate on batteries. The line voltage versions are the larger and more recognizable versions used in motion picture lighting, architectural, and night sky based advertising. The battery versions are usually flashlights of no more than 70 watts. While xenon flashlights do have boosting circuits, they presently do not allow connection to anything other than 12 volt batteries and the output voltage varies with input voltage. These same flashlights operate from 13.2 volts, the fully charged voltage of the 12 volt batteries, down to about 11 volts where the flashlight shuts off. This leaves an enormous untapped potential in the battery.
Car batteries, which are likewise nominally 12 volts, generally have about 1 kilowatt-hour of capacity. If a car battery, through a power supply, were used to power one of the larger fixtures, battery life would be objectionably short. For example, a fixture with a 4 kilowatt xenon bulb could only operate for 15 minutes. This is one reason no large xenon lights are battery powered.
In addition, xenon lamps have a zener diode-like characteristic in that, when a xenon lamp is operating, even small changes in lamp voltage result in disproportionately large changes in current. Accordingly, ballasting is typically employed to limit the electrical current applied to a xenon lamp. Thus there exists a need for a battery operated xenon power supply, which provides ballasting of bulb current and allows a greater portion of a battery's charge to be extracted before recharging than do present systems.
Light Emitting Diode (“LED”) lamps have traditionally been used for indicators and displays but just recently have evolved into primary illumination sources. This evolution has accompanied the advent of new colors, and brighter LED lamps. Groups of these new and powerful LEDs have recently been integrated into fixtures and have become capable of lighting broad areas with useable levels of light. These devices require a large DC source of power to operate in a non-flickering mode. They are also very sensitive to over-current conditions, which can easily destroy the devices. The voltage required by these LED fixtures depends on the number of individual LEDs that are connected in a series combination inside the fixture. The voltage and current to these fixtures vary with temperature and from device-to-device. Consequently they must be ballasted or regulated to keep a steady output. At present, battery based applications for LED fixtures are primarily for emergency lighting. Initially these fixtures do an adequate job of illuminating, but as the batteries run down, the light intensity fades. This is one primary reason battery based LEDs are not regularly used for illumination in motion picture and photography lighting situations. Photography can't be precisely practiced with slowly dimming light levels.
There have been a few attempts to run small LED devices on batteries with simple series voltage regulators in-line with the battery. These systems are very inefficient and when the battery discharges even slightly, the circuit begins to dim because there is not enough voltage in the battery to make up for the regulator voltage drop as well as other losses. One could include a larger number of batteries to provide more head room for the regulator, but the higher voltages would cause efficiencies to drop even lower due to increased heating of the regulator. Also the size and weight of the batteries would become unmanageable.
In addition, there are numerous fields in which it is either difficult to match a battery voltage to the requirements of an appliance, or the appliance is intolerant of the diminishing voltage of a draining battery. For example, motion picture and television cameras generally work on rechargeable lead acid or NiCad type batteries. These batteries are used until the voltage drops from an initial 13.2 volts down to between 10 and 11 volts. At that point there is an enormous potential of electricity left but unusable in these batteries. Cameramen typically have multiple sets of batteries used in rotation. Some in use, some being charged, and some waiting as ready. Not only is this number of batteries an expensive proposition, the management of this number of batteries is time consuming, creates logistic nightmares and is otherwise just generally problematic.
Direct current motors are often connected to batteries. This type of configuration is generally used with motors for displays, servos, hydraulic pumps, trolling motors, portable tools, and vehicle-mounted winches. When used with motors, some battery circuits are run through speed control circuits, but otherwise connect directly to the battery. (Trucks and farm machinery have the advantage of constantly recharging their batteries from a running internal combustion engine). Even in this situation, however, the battery voltage can lag during a high cycle use of the motor. And of course, as the voltage goes down, so does the motor speed, and/or torque. This is clearly evident when using a battery-powered man-lift. As the battery fades, the lift's moving ability becomes less and less until the operator has no choice but to return to the ground, assuming, of course, that there is sufficient power to lower the lift.
Many DC motor driven devices use multiple, series connected batteries to raise the capacity of energy available, while decreasing electrical current through motor, which will extend the usage in both time and torque. The down side of this is that companies often have to make similar and somewhat redundant versions of a particular product line to operate at these different voltages. Added to that, these similar versions may be accidentally confused with one another and consequently connected to incorrect voltages that may destroy the motor or its controller. These multiple-battery configurations also have the added problem of the weakest link. It is well known in the art that the weakest cell may actually reverse charge during normal use, further lowering the voltage available to the motor. As with a single battery, when a the collective charge of a series of batteries is discharged to the point where the motor's performance degrades, there is a great deal of energy left in the batteries that can not be tapped by existing techniques.
This problem can also be found in battery-operated tools such as drills, saws, sanders, and the like. Well before the battery charge is fully exhausted, but after the voltage has dropped a few volts, the motors of such devices will not develop enough torque to make the tools usable. As in other areas, spare batteries are often kept on hand so that a set can be charging while a set is in use, and perhaps, a charged set stands ready for use. The investment in batteries can dwarf the investment in the tool itself.
Thus it is an object of the present invention to provide a battery operated electronic power supply, which can provide a constant output voltage over a substantial portion of the battery charge.
It is a further object of the present invention to provide a battery operated electronic power supply, which provides a constant power source for LED based illumination systems over a wide range of battery voltages.
It is still a further object of the present invention to provide a battery operated electronic power supply, which provides a constant power source for DC motors.
It is yet a further object of the present invention to provide a battery operated electronic power supply, which provides a ballasted, constant power source for operating a xenon light.